It's not necessary to deconstruct and reconstruct a pte every time its
flags are being updated.  Introduce pte_set_flags and pte_clear_flags
to set and clear flags in a pte.  This allows the flag manipulation
code to be inlined, and avoids calls via paravirt-ops.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>